


Learning Curve

by japanfan101



Category: Undertale (Video Game)
Genre: Angst, Bondage, Experimentation, Fluff, Other, Porn With Plot, Reader has a vagina, Reader has no defined gender, Reader-Insert, Smut, Talk of Suicide, Tentacles, after that it's all consensual, dubcon, sort of but only the first time, starts in chapter 2, though only briefly and not elaborated on
Language: English
Status: In-Progress
Published: 2016-01-30
Updated: 2016-04-01
Packaged: 2018-05-17 02:25:21
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 9
Words: 18,173
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5850280
Author URL: https://archiveofourown.org/users/japanfan101/pseuds/japanfan101
Summary: <blockquote class="userstuff">
              <p>When you fell into Mt Ebbott, you didn't expect to survive. However as it turns out, you did. Somehow. When you wake up you don't know where you are, but luckily Dr. W. D. Gaster is there to explain it to you and learn from you.</p><p>Sometimes, though, you wish that fall had actually killed you.</p>
            </blockquote>





	1. Waking Up

When you came to, the first thing you noticed was the dim light glinting off of the pristine, white walls. You felt cold metal against your back and the room smelled very… sterile. Almost like a hospital. Was that right? The last thing you remembered was the fall, and tumbling down into a hole that led to the inside of a mountain. Was that all a dream? If it actually had happened, were you found and rescued?

Attempting to sit up proved impossible, as you discovered your arms and legs were strapped to the freezing surface beneath you. _What in the world happened…?_ As best as you could, you glanced around to see what you could see. There was a long table against the wall to your left, the top was cleared off completely and a sink sat in the middle. There were drawers beneath it, all labeled. Unfortunately the writing was too small to read from where you were laying.

To your right, a few tall cabinets with glass doors lined the wall filled with a variety of different vials and bottles filled with god knows what. The bottles all had labels on them but, again, the writing was far too small to make out. You weren’t hooked up to any machines, so despite the appearance and feel of the place this probably wasn’t a hospital.

A video camera was set up in the corner of the room, up by the top of the door. The thought of someone watching you like this made you shudder. Wondering if there really was someone watching, you called out while looking directly at the camera. “Um… Hello? Can someone tell me what’s going on please…?”

It took only a few seconds before you heard a knock at the door, which swung open immediately after. The man… thing… that walked into the room wasn’t human. He… or it, was tall, very very tall. Almost 7 feet tall it seemed like… He looked like a skeleton, but he was /moving/, so that couldn’t be right…! What the hell was he? The lab coat he wore swished behind him as he walked closer to you, a hint of excitement in his eyes.

“Ah, I see you are awake now. My name is Dr. W. D. Gaster, you were found and collected after falling down here. It is quite rare for a human to fall into the underground.”

When he reached out to you, you tried to squirm away but couldn’t thanks to the restraints. “W-w-why am I tied up? What is this? What do you want? P-please, please don’t kill me, I didn’t hurt anyone. I want to go home, please…”

His hand rested lightly on your right ankle and undid the strap holding it down, then moved to your left ankle and undid that one. For a split second, if you didn’t know any better, you’d have thought he looked amused. “We don’t intend to hurt you. The restraints were merely to ensure the safety of everyone here, I hope you understand. I realize that you haven’t hurt anyone, however precautions must be taken until I can be sure.” His eyes scanned your body while his hands furiously scribbled down notes. He mumbled quietly to himself, seemingly distracted. For the first time you realized you were naked.

“C-can I at least have my clothes back…? Please? I-I-It’s a bit cold in here and… and I’m uncomfortable.” He seemed fairly reasonable, professional. You hoped that he’d be at least accommodating, though as long as he didn’t kill you, you supposed you could put up with just about anything. _All the same, some cover would be nice…_ Your face was flushed a light red.

Not pausing his notetaking, he nodded. “Of course, I just have to conduct the first examination. Afterwards your clothes will be returned to you.” His eyes turned to purple flames as a few ghostly hands materialized and you had to bite back a scream, regardless of this man’s professionalism you were terrified. What was he going to do? Would he hurt you? Desperately, you tried to wriggle away as the hands approached. “Human, please try to stay still. You won’t be harmed, I merely wish to learn. If you don’t hold still, I’ll be forced to replace the straps.” Swallowing hard, you hesitantly stopped moving as stayed as still as possible.

Still, you heard your heart beating loudly in your chest and jumped on reflex when one of his hands touched your calf. Desperate to keep your legs free, you muttered an apology under your breath hoping that he either didn’t notice or would let it slide.

His hands poked and prodded you, but it never hurt. At worst, it felt uncomfortable. In all honesty, if you weren’t so terrified and still had your clothes on, this would feel like a normal examination… just as he said. Still, you were having a hard time breathing from the fear.

By the time his hand stopped writing and the other hands dissipated, your heart had calmed and your breathing returned to normal.

“Thank you, human. Your cooperation is invaluable to me and my staff.” He smiled kindly at you, and returned his clipboard to a pocket inside his lab coat. “I will return shortly with your clothes, and then you will be shown to your room.”

 _Room?_ You shivered. “W-wait, room? How… how long will I be here? Why am I here?”

He looked surprised, “oh, was that not clear? We wish to learn about humans by studying you. You will remain here until I’ve learned all that I can.”

You didn’t answer, but were panicking internally. Even humans don’t understand everything about how humans work! You’d be here for the rest of your life if that was truly his goal… What about your family? Your friends? What was he, anyways? Why did he want to learn about humans? And why did it have to be you, of all people! That fall should have killed you, so why were you here? Was this some kind of trippy lucid dream? It all felt incredibly real…

When you didn’t answer, he left the room and returned shortly after with your clothes. He undid the straps on your wrists and helped you stand up. This strange man wouldn’t even look away as you dressed yourself, and it made you incredibly uneasy… then again, he probably didn’t even understand why you asked him to look away in the first place.

Gaster himself escorted you to your room, in relative silence. His hand rested around your shoulder, firmly. He was most likely making sure you didn’t try to escape. The two of you passed other… creatures, but they all turned their heads down and moved to the opposite side of the hall, walking faster. Were they… scared? Scared of you? Gaster had said something about keeping everyone safe… Did they think you were going to hurt them? The thought made you feel sad, somehow. What had happened to make them all so fearful of just a single human?

The guards at the door opened it, and Gaster walked you inside. “We brought some of your belongings here, the ones that fell with you. Unfortunately, anything that could be dangerous was locked away safely and won’t be returned.” He motioned to some shelves on the wall, your backpack sat on one of them near eye height. The walls were all white, and there was a door that hung open leading to a bathroom. A bed rested in the corner with tan sheets, blankets, and pillows. To the right of the bed was a bedside table, with a clock and small red button on it. The floor was also a light tan. _Tan’s not the most exciting color, but at least it is a color._ “If you need anything, feel free to knock on the door and the guards will help you. In an emergency, the button near your bed can be pressed and I will be alerted immediately. For the time being, you aren’t allowed to leave this room. Meals will be brought to you regularly along with water. Do you have any more questions?”

“Y-you… Um... Can I ask… What are you? I-i-if that’s rude, then I’m sorry, I won’t… uh…” You looked down at the floor, voice trailing off.

“I, along with my staff, am a monster. We live here in the underground, separated from humanity. It’s no wonder you weren’t aware.” He smiled reassuringly, resting a hand on your shoulder in an attempt to ease your fear. “You don’t have anything to fear from me, or anyone else here.”

Something snapped inside you and you pulled away from him roughly, “but… you want to run experiments? How can you say that you won’t hurt me or that I shouldn’t be afraid? You kidnapped me, tied me up, and then ‘examined’ me like I’m some lab rat! Don’t you have some kind of board of ethics?” Your voice was quiet, but the anger it held was unmistakable. “And everyone else here seems to hate me or something, why not just kill me if I’m so dangerous?”

For a few seconds, there was no response. Gaster walked in front of you and knelt down slightly, looking you in the eyes. “I understand how scared you must be. Everything is going to be okay though, I won’t hurt you and no one else here will either. You’re invaluable to us.”

You snort, “So the benefit outweighs the risk, then? Fine, whatever. I’ll play nice, but I don’t trust any of you. Nor will I ever even consider trusting anyone here.” With crossed arms, you turned your back to him. “Plenty of scientists are like you. Pretending to be kind, however all you care for is discovery. No matter how many people suffer for it. Never mind that I’m a sentient, living person, just like you and everyone here. I’m just some human to learn from in your eyes. I’m not invaluable either, more humans could fall down easily.” Your words seemed to be filled with anger, but more than anything you just wanted to say whatever you could to make him leave so you could be alone and he wouldn’t see you panic.

Standing up, he nodded. “I’m sorry that you feel that way. I assure you, I do view you as a person; however I likely can’t convince you of that right now. Please, get some rest. My assistant and I will bring you food and water within the hour. If you need anything else, all you have to do is ask and we will do what we can.” Gaster turned back to look at you and smiled softly before exiting the room.

After he left and you heard the lock on the door click, you collapsed to the floor, trying to relax and reminding yourself to take deep breaths. _It’s okay, I haven’t been hurt yet, I can easily deal with this._ Your breathing calms and, shakily, you stand and move to your backpack.

_That’s right… I had just gotten out of classes. It was a last minute decision to hike up the mountain and throw myself in. How did I even survive…? I didn't plan for that._

In your backpack, there were mostly just textbooks, notebooks, a sketchbook, and a few pens and pencils. Your knife was nowhere to be found, but your phone was there, unfortunately with a dead battery. _Probably useless here anyways, since there’s most likely no signal._ You pulled out the sketchbook and your pencils then went to sit on the bed, deciding you might as well draw while waiting. If nothing else, you figured it’d take your mind off of what was happening.

When Gaster returned, there was a much shorter yellow monster with him. She looked like a dinosaur almost, albeit a small one.

“U-u-um, h-hello, I’m… I’m Alphys.” Her voice was shaking and you felt bad, even though you hadn’t done anything. She was obviously afraid.

Gaster introduced her as his assistant, and said that if he was busy but you needed anything, she would be the one helping you. Throughout all this, you only looked up once before returning to your drawing; when Alphys introduced herself. A few moments of silence passed before Gaster decided you weren’t going to answer, and he placed a tray of food and a bottle of water next to you. With that, he told you to rest up and try to get used to things over the next few days.

They both left, and only once you heard their footsteps receding did you reach for the food and hesitantly take a bite. Surprisingly, it was… pretty good. You ate it all very quickly. Unsure of where to put the tray, you ultimately decided to move the clock to the side and set the tray next to it.

 _This was a stupid decision…_ Exasperated, you sigh. _Well I’m here now I guess… might as well try to play along and cooperate._ You yawned loudly, and put your sketchbook and pencils on the ground next to the bed. It had just dawned on you how tired you actually were. Laying down on your side, you quickly fell into a deep sleep.

**Notes for the Chapter:**

> So I know stuff like this has been written before but I... er... well it's really an idea I enjoy. XD This story will be long, and I dunno exactly where I'm going with it yet, honestly. But it'll be good, I have a few minor plans for it.
> 
> Also I suck at naming. Honestly. The hardest part of this fic was deciding on a relevant name. I apologize for having such bad story names.
> 
> If you have any experiments you'd like the good doctor to perform, feel free to send suggestions my way! ;)


	2. Human Reactions to Stimuli

**Summary for the Chapter:**

> Gaster tests what sort of reactions humans have to various stimuli. This chapter has smut towards the end, just so you know. Feel free to skip it, it's not really important for the story.

A few weeks had passed since you woke up in the lab under Dr. Gaster’s care. So far he hadn’t performed any experiments on you, which surprised you. Instead, he spent the time helping you feel more comfortable. He introduced you to his other assistant, and younger brother, Sans. He also showed you around the lab, took you to the library there to grab some books, and tried to acclimatize you to the underground.

You were beginning to feel almost safe here, and that scared you. You knew that that could go away in an instant. When Gaster tried to get you to speak, you said nothing. Asked no questions, answered none, you wouldn’t even tell him your name. To be frank, he scared you. Somehow you felt like he was much more dangerous than he let on. Even though he’d told you more than once that human souls are stronger than monster souls, and you’re in no true danger here, you still didn’t trust him.

The food was good, though, and you were given nearly everything you asked for so long as it wasn’t harmful. It was hard for you to keep being afraid, but you didn’t want to trust them. You couldn’t, you wouldn’t let yourself.

It had been a month since you fell when Gaster returned to your room and asked if you’d be comfortable letting him examine you again, but more thoroughly this time. You were uncertain, but decided that it was just a simple examination; he wasn’t going to hurt you and you’d be helping a lot. Plus you felt… guilty, almost. Living here but not giving them anything back. It’s true that most of the monsters still feared you, but when they did talk to you they seemed kind and showed no malicious intent.

You answered him, talking for the first time since the first day. “Y… yes. That’s fine, I don’t mind.”

There was an eager glint in his eyes as he led you back to the examination room, the same place as before. Sans rolled a cart in with various supplies, and then was shooed out by Gaster. It was almost cute watching how they interacted; normally, Gaster was very serious and had an air of importance and elegance about him. But when he was with his brother, he seemed to be much more laid back, even making jokes with Sans sometimes.

On the cart that was rolled in, the instruments that stuck out to you were vials and needles to take blood. The sight of them made you cringe slightly. You’d always disliked needles. There were also a few instruments you didn’t recognize, along with lots of various, small containers. Most were only a bit bigger than the vials for your blood. You couldn’t help but wonder what he had planned.

“Today should be fairly simple,” He pulled out his clipboard and pen, “I want to get a basic idea of how your body reacts to various stimuli, along with taking a few samples. None of this should hurt, however it won’t necessarily be comfortable the whole time.”

You nodded in response, “okay… Uh… I’m gonna warn you right now, as I do with everyone who draws my blood… I’m kind of a baby about needles. There’s… there’s a vein in my arm that’s really good for it though, so you shouldn’t have to poke more than once…” You didn’t particularly want to talk to him, however if you didn’t communicate that he wouldn’t know and there might be more problems than either of you expected.

“Thank you for informing me,” Gaster started putting on a pair of gloves, then paused, “oh I almost forgot, since you seemed uncomfortable last time I arranged something to help with that.” He moved to one of the drawers in the table and pulled it open, when he stood back up he was holding some folded up cloth. “This came from the surface. It has been sewn back up and sanitized, I thought it might make you more comfortable.”

You took it from Gaster and found that it was actually a simple hospital gown, and you unconsciously smiled at him. “Thanks, that’s… that’s actually really cool of you.” He just nodded and finished putting his gloves on as you stripped out of your own clothes and put the hospital gown on. It wasn’t the most comfortable, but it covered you and you didn’t feel quite so vulnerable.

“Now, if you would have a seat we’ll begin.” Nervously, you sat down on the table in the center of the room that you’d been strapped down to before. “Since you said you find this experience unpleasant, I’m going to go ahead and draw some of your blood before anything else. Is that all right with you?”

“Y-yeah, let’s get that out of the way… thanks.”

In silence, he prepared everything. When he did finally take your blood, you were relieved that he managed to get the needle in the vein on the first try. It didn’t take long for all three vials to be filled. He was gentle throughout the entire process, which helped to calm your nerves.

Gaster took samples of your hair, skin, and saliva as well. After all that was done he asked you politely to lie down, which you did. He himself sat down in a chair near the cart.

“Now human, during this process, I want you to tell me anything and everything you feel, that will help ensure that I interpret your reactions correctly. Okay?”

After you assured him you’d do that to the best of your abilities, his eyes began to glow purple as one hand materialized in the air next to you. It was surprisingly close, so much so that it startled you. You had almost forgotten about the rest of the examination, and grew incredibly self-conscious at the thought, uncertain about what he had planned and how you would react. Still, you said this was fine earlier and you did want to be helpful.

The disembodied hand ghosted over your chest, causing you to shiver. With one finger, it traced gently down to your belly button and paused, pressing down lightly. “Hmm…” He mused, “I saw something interesting here when I first examined you. What is it called? And are you aware of its purpose? None of the books I've read on humans have had that particular detail.” His eyes turned to your flushed face.

“Well… yeah?” You were confused as to why he was asking. You told him what a belly button was though, and what it was for; how it doesn’t do anything for humans after they’re born, as far as you know. He scribbles down information quickly, nodding and murmuring to himself here and there. After your explanation was finished, he thanked you and continued.

A few more hands materialized; one moved down your side softly, tickling you and forcing you to hold in a laugh. It must have been obvious, because Gaster frowned in response, “please, don’t try to consciously control your reactions. For this to work, I need to see how you react naturally.” Embarrassed, you mumbled a quiet apology. A third hand rubbed your right arm, moving from the top to the bottom, probably trying to map out muscles or just get a feel for the arm in general; you weren’t really sure.

The other two hands rested on either side of your hips and pressed on the bone there a bit too hard, making you wince slightly. “That’s a bit uncomfortable…”

“Does it hurt?”

“Well… Not really, I guess, but it definitely doesn’t feel good…” With a nod, Gaster’s hands let up slightly but still ran along the edge of the bone. The hand on your arm moved to your other arm, and it almost felt like it was massaging you. Somehow this was all… really relaxing. You sighed softly, he didn’t seem to hear though. His hands roamed all over your body, mostly just trying to get a feel for your reactions. This whole experience was oddly pleasant... he never once hurt you, even accidentally. The hand that was on the left side of your hip moved up to your chest, and gently cupped your breast. You squirmed slightly in his grasp, noticing him look at you curiously. “It’s… uh… I was just surprised.”

One of his hands brushed against your crotch, making you jump and gasp quietly.

He looked up at you and his hands stopped moving. “Are you okay?”

Flushing, you nodded.

“Why did you react that way? How are you feeling?”

No, there’s no way you were going to tell him that you enjoyed this. There’s no way. Hell would have to freeze over before you told him that this was actually turning you on. “N-n-no, it’s nothing, it’s nothing.”

If he had eyebrows, one of them would be raised at you skeptically. “Oh?” His hand went between your legs and stroked you gently, which caused you to take in a deep, shaky breath and unconsciously try to press into his hand. “I wasn’t aware that’s what nothing looked like.”

You shook your head, face growing redder. “I-it’s nothing, I swear, please just leave it at that, please… This isn’t something you n-need to know about humans, s-s-so…” He rubbed his hand up and down, more insistently, cutting you off and pulling a needy moan out of your throat.

“It doesn’t seem to hurt you at all…” Gaster mumbled, writing something down on his clipboard. When he looks back up at you, his expression is genuinely puzzled. He really doesn’t seem to understand what he’s doing to you. “It isn’t exactly up to you to decide what I do and don’t need to know. Now, please share with me what you’re feeling.”

His hand stopped moving and you had to bite your bottom lip to keep from complaining about the loss of contact; it felt so good and you wanted… _No, no! No. This is nothing to get excited about. Calm down._ You took in a deep breath and averted your eyes. “I-it didn’t… it didn’t hurt… Um…” You paused, considering your words very carefully. “T-that’s just a… a sensitive spot. And that… felt… well it felt good, but not… it’s not just that.”

“What do you mean? If it didn’t hurt, then why did it seem to bother you so much? I’m afraid I don’t understand.”

“Humans are just… shy about… that sort of touch. B-because… it’s… uh…” You felt like your face would catch on fire if it got any hotter. “It’s a sexual thing. D-do you get it? I don’t even know if that’s… something that… that monsters do too. Basically that’s a part for… reproduction.”

“Hm.” Gaster took note of something, then turned his purple gaze towards you. “May I explore this a bit?”

You bit your bottom lip. “Do I have a choice…?”

He paused to think for a moment before responding. “Well I do want to learn about this, so if we don’t take care of it now I’ll ask you again in the future. However we have enough time, I’d be okay with putting it off for now. I would really like to learn about this as soon as possible, though. It’s quite interesting.”

A shiver went down your spine. You weighed the pros and cons; if he took care of his curiosity now, he likely wouldn’t go this far again. But… you really weren’t comfortable with this. All the same, it did feel amazing, so… With a gulp, you nodded. “Go ahead, then…”

Gaster smiled brightly at you, “thank you, I appreciate your cooperation.” All but one of his floating hands dissipated, the one between your legs staying in place as he wrote something down. You tried to mentally prepare yourself, but before you could his hand was caressing you again. Figuring you might as well relax and enjoy it, you closed your eyes and kept your breathing steady.

Despite this being an examination, and experiment, Gaster was very gentle and careful not to hurt you. It drove you insane. His feather light touches against your groin combined with the fabric still in the way made you whimper in frustration, needing more. You opened your eyes, “D-Dr. Gaster, you don’t… you don’t have to be so gentle…”

Purple orbs met your eyes, “I don’t want to hurt you.”

“No, that’s not what I mean...!” You whined, “a-at least…” Unable to actually say what you wanted, you reached down and pulled the hospital gown up to your waist. “I-I-I… I would think you want to actually observe… Or… something.”

He stood up. “Here, please don’t be alarmed but I do believe this will be more helpful.” The final hand disappeared, and he helped you sit up and take the hospital gown off. You shivered from the cold air.

Before you could ask what he was doing, six dark purple tentacles shot out from his back. As you gulped and your eyes widened, four of them grabbed your arms and legs, holding you up in the air spread-eagle. “U-u-um… This… Is this necessary…?” Not that it didn’t excite you. You couldn’t help but wonder how he would use the other two tentacles. You had a few ideas about where you wanted them if he didn’t know what to do with them, though...

“Not necessary, however it is much more useful for me.” His eyes looked you up and down and you gulped. Gaster sat back down and pulled you towards him, making sure he could see everything. As if you weren’t embarrassed enough already.

Without much warning, one of his ghostly hands returned and went back between your legs. “Seeing as you’re rather… unfocused, I will reiterate what I said earlier. Please don’t hold back. I want to see your natural, immediate reactions.” Gently he pulled the folds back to examine what was there, starting to write on his clipboard again. Experimentally, one of his fingers brushed across your clit, making you gasp and shudder. “Hm… What’s this?” Your head fell back and you moaned as he rubbed against it harder, noting down your reaction. “It seems to be incredibly sensitive. Interesting…” His voice trailed off as he continued to write.

You squirmed in his grasp, trying to get him to do more, but he held you firmly in place and didn’t move until he finished writing. Gaster ran his finger down to your entrance, which caused you to jolt in response to the unexpected movement. He quickly scribbled something down before bringing his hand back to him, curious.

“This is fascinating!” He was looking at the fluid on his finger with a look of excitement and curiosity on his face. An empty vial floated over to him, and he materialized a second hand to hold it beneath your entrance as he sat back down. For a moment, you thought about telling him that you could explain that so he wouldn't have to collect any; before you could get a word out, however, the other hand pinched your clit between two fingers, which made your mind go blank for an instant. A moan passed through your lips.

“Gaster, that feels so goooood~” Despite your attempts to press against his hand more, you couldn’t move a centimeter thanks to the tentacles holding you in place. Within seconds, you were breathing heavily and your moans increased in frequency and sound. When he stopped you tried to calm your breathing, and when your head finally cleared you felt like you could die of embarrassment. It felt good and you wanted to ask him for more, beg him not to stop, but you refused to sink that low. For the moment, anyways.

You were able to see that the pause was because he’d collected enough of your fluid and was labeling the vial, setting it aside with the other samples. Tentatively, he pressed a finger against your entrance. “It’s quite warm…” He seemed hesitant, uncertain whether or not he was supposed to do this.

Impatiently, you groaned and desperately tried to press down against his finger. Gaster seemed to get the idea after that, and he slowly pushed his finger inside you as far as he could and held it there as he took a few notes. You sighed when he entered you, but wanted so much more. Quiet noises escaped your lips.

When his full attention returned to you, and his finger started to slowly explore, you let out a needy whine. He was taking notes the entire time, occasionally muttering to himself about something that caught his interest. It was impossible to move, you were trapped, suspended in the air. His finger worked itself inside of you, occasionally sliding out about halfway and pressing back in. It felt good, and drew gasps out of you, however it was nowhere near what you needed. “Mmm… Gaster, that… Hah… It feels good, but…” You couldn’t bring yourself to finish that sentence.

“What is it?” He asked, not even looking up at you. His finger slowed however, and you made a small disappointed noise.

“T-that’s… I… I need more than that…”

“What do you need?”

Your face flushed an even brighter red, “u-uh…” You swallowed hard, unwilling to say it. “N-never mind…”

Gaster seemed puzzled, but he continued taking his notes as if nothing had happened. His finger did speed up inside you though. Shortly after, he hit your g-spot rather hard and you couldn’t hold back a loud cry. He instantly stopped and looked at you, concerned. “Are you all right?”

With a whimper you managed a weak nod, “d-don’t stop, please, Gaster don’t stop…~”

However, instead of doing as you wished, he pulled his finger out of you and left you feeling empty. One finger wasn’t much, but it was better than nothing. You were dripping wet and on the verge of begging him to fuck your brains out, he’d been unintentionally teasing you for what felt like hours.

“I have one more thing to try. After that, I’ll do this however you want me to for as long as you want. Please, be patient.” He smiled warmly but you only sighed, frustrated.

“W-whatever it is, just hurry…” The ghostly hands disappeared and one of his tentacles approached you. It was bigger than you thought at first, and bigger than anything you’d ever used; it would have been intimidating if you weren’t so excited. You felt heat rushing through you in anticipation.

“This may be uncomfortable initially, however I think you’ll be just fine from what I’ve seen.” As it pressed against you, a shudder rippled through you. It felt big, but the slight flash of fear faded as it pushed inside of you slowly, with surprising ease. You moaned loudly and took a few shaky breaths. Fire was coursing through your veins, and it felt so damn good.

Once it was fully buried in you, it stopped moving altogether in order to get you used to it. Panting, you tried to press against the tentacle for more pleasure, however you were still being held in place and couldn’t move. Gaster was writing something down; you let out a frustrated groan, “Gasteeeeer please, move already…!”

“All in due time.” You thought there was a small smirk on his face as he said that.

By the time he finished writing, your face was a dark red and sweat beaded your forehead; you were about to start really, truly begging when, without warning, his tentacle pulled almost all the way out and pushed back into you deeply. You let out a loud, surprised cry as your back arched.

You felt it squirming around inside you, rubbing against your walls and sending wave after wave of pleasure throughout your body.

“I think I have all the information I need for now, human. But you did such a good job, and I did promise to continue this as long as, and however, you wish.”

Moaning loudly, you clenched your eyes shut. “I-I-I justooooh fuckfuckfuuuuck, there, right there!” He hit a particularly sensitive spot inside you, and you felt like you could spontaneously combust in that moment. Another, much smaller and slimier tentacle inched near you and, once close enough, pushed on your clit and seemed to pull it inside itself. The squeal in your throat turned into a loud yelp as the smaller tentacle started to suck lightly.

Drool dripped down your chin and your head was thrown back as you released another loud cry; the tentacle inside you pounded you even harder than before as the smaller one started to wriggle around your clit. It felt like there were small nubs inside it, and the feelings were making your mind go numb.

The air in the room had grown hot, and you could hardly breathe as your heartbeat pounded in your ears. Your entire body tensed up and the waves of fire washing over you began hitting you more quickly, until they were coming one after another with no break in between.

“Gaster, oh god, Gaster I-I’m right there…” You managed to gasp out between the loud, pleasured sounds pouring out of your throat. Almost seconds after the words left your mouth, your vision went white as you came, loudly and messily.

Gaster had slowed his movements but not entirely stopped, and you had to let him know that was enough and that it was overstimulating. Looking a tad embarrassed for once, he stopped and laid you back down on the table gently, retracting his tentacles.

He waited until you caught your breath before cleaning you up and asking questions about what just happened. You had to explain, through shaky breaths, what an orgasm was and such; though you could barely keep your eyes open. Gaster seemed to catch on fairly quickly and decided to save the rest of his questions for later. He helped redress you, but you passed out before you could walk yourself back to your room. He carried you back and laid you down in your bed, then went off to work on analyzing everything he'd collected.

**Notes for the Chapter:**

> Ooooh my god I almost died writing this. *ahem*. Anyways. Hope it's not terrible, I started it hours ago and just finished it. The time's like 2 am so if this chapter's crappy, that's why :p I'll probably re-read it in the morning and fix some stuff up.
> 
> Anyways, send me suggestions if you have any!


	3. Chapter 3

**Summary for the Chapter:**

> No smut this chapter, sorry guys! I want to put in some plot and spend time thinking up new, fun experiments~

The next few days passed in relative normalcy. Gaster had started to take your vitals every morning; blood pressure, temperature, etc. You eventually got used to it, though it wasn’t ever much fun. Most days he would bring you your meals, though when he was busy, you’d get a visit from Alphys instead. You and her talked a little bit every time you saw each other and, though she still seemed shy and uncomfortable, she was starting to get more comfortable around you. The times you saw Gaster, however, were much less enjoyable. Not because of anything he said or did. He was still as professional and polite as always, occasionally even asking if you’d go to the cafeteria and eat with him. You turned him down every time.

Hell, you couldn’t even stand to look at him!

Not because you hated him, god no. He still scared you, that much is true, but he’d been nothing if not kind to you the entire time you’ve been here. No, you were embarrassed and ashamed.

Remembering what happened during that experiment still caused your breath to catch in your throat and turned your face bright red, like a tomato. Gaster never mentioned it again, and if he noticed your discomfort he said nothing.

It was nearly impossible for you to talk to him without stumbling over your words, or mumbling so quietly that he couldn’t hear.

Since Gaster never talked about it, and didn’t seem any different, you knew that it had been nothing more than an experiment to learn about humans, a test rooted in curiosity. He wouldn’t understand why it bothered you so much.

Sitting on the edge of your bed you let out a loud sigh and flopped over onto your side, head landing on your pillow. It was almost time for your next meal to come, and you were incredibly nervous. A knock resounded in your room from the door and Gaster stepped in after a few seconds, closing the door behind him. “Good afternoon, human.” He approached you and you sat up, looking at a very interesting spot on the floor. “I was hesitant to say anything, however if I wait much longer then progress will slow. May I ask what’s been bothering you?”

You shook your head frantically, still not looking at him. “N-nothing…”

The bed creaked as he sat down next to you, making you scoot away as far as possible. “Are you ill? You haven’t had a fever, and your vitals have all been normal, but perhaps it’s something I’m not aware of.”

“I’m… I’m not sick.” You swallowed hard, trying to forget what had happened.

His hand rested on your cheek and tilted your face up to meet his eyes. You pulled away from his hand and looked back at the ground. “If there were nothing wrong, you would have no problem looking at me.”

Cringing, you hesitantly nodded. “W-well… you’re… you’re not wrong…” Feeling guilty for putting his research on hold over something so minor in his eyes, you continued quietly. “I get that… what happened was nothing more than an experiment. But…”

Silence filled the room for a few moments, Gaster waiting patiently for you to explain.

“It’s… that was something humans only do with each other if… if they’re… uh… intimate. And… I just… I feel like I could die of embarrassment…”

He processed what you said, then carefully answered. “I… wasn’t aware of that. If I went too far, I apologize.”

You shook your head quickly, “no, I said you could and it’s… fine. Just wish that I had more self-control…” Towards the end of your sentence, your voice got quieter until it was barely a whisper.

“There’s nothing to be embarrassed about, you simply did as I asked.” His hand rested on you shoulder and you could feel his worried stare, you flinched at the touch but didn’t pull away. When you said nothing, Gaster sighed. “There are two very important reasons why I’m not going to leave you alone to worry over this. First, I want you to be as happy and healthy as possible here. I’m grateful that you haven’t hurt anyone. If another human had fallen, that would likely not be the case, so I’ll do what I can to keep you from being miserable here. Secondly, there is still much for me to learn, but I can’t run any experiments with you like this. What do you need in order to relax when I’m around?”

“I dunno…” You shifted awkwardly, face red. Though that was really the norm these days.

Gaster pondered something before talking. “Will you come and eat with me today? It isn’t healthy to isolate yourself.”

“I’d… rather not…”

“Okay. Wait here for a moment, I’ll be back with your lunch.” With that he stood up, rather abruptly, and left the room. When he returned, you hadn’t moved an inch. He was carrying one tray and had two of his magical floating hands were holding another. “Here.” He handed one tray to you and sat down next to you with his own.

You furrowed your brow in confusion. “Uh…”

“I’ll be eating in here today.”

It was impossible for you to do anything but nod in response. Why was he going this far…? Whatever, it didn’t matter. You just wanted to get this over with. The knot in your stomach, though, made it impossible to eat more than a few bites. With a sigh, you put your unfinished tray of food on the bedside table.

Gaster stopped eating and spoke up. “I don’t wish to pry if it makes you uncomfortable. But I am here to help, please remember that. I’m on your side.” He smiled at you, no doubt trying to comfort you.

His words just made you feel sicker. You felt guilty, he seemed genuinely concerned for you. Noticing that, you felt your heart drop. Despite all that had happened… you weren’t unhappy here. Nervous, embarrassed, sometimes scared. But not unhappy. You had little to worry about, and could do just about anything you wanted. You sat up straighter and turned to him with a timid smile. “Yeah… I know. Thank you. I’m not unhappy here or anything… Sorry for being so strange, I… I don’t mean to worry you or anything…” You mumbled the last part, hoping that didn’t come off as presumptuous.

The kind expression on his face now held a hint of surprise. “It’s quite all right, I just want to make sure your mental health is stable as well as your physical health. Please tell me right away whenever you are struggling, okay?”

“I will, no worries. Sorry again…”

He ran his thumb gently down the side of your face, making you shudder and reddening your face further. “It’s no problem at all.” A calm smile graced his face, seeing it made you feel at ease. The rest of the meal passed in relative silence. He did see your sketchbook and ask what you’ve been drawing, so hesitantly you showed him. Nothing was a finished piece of art, they were all just sketches, but he told you that he thought they looked nice.

After you both were done eating, he stood up and stacked the trays on top of each other. “I have one last thing to tell you. You seem to be fairly acclimatized and the rest of my staff have gotten used to you as well. You’re allowed to leave your room whenever you like. There are certain places you aren’t allowed in, most are places that would be dangerous for you, however you may roam the majority of the lab.”

That excited you a bit. You’d only been allowed to leave if Gaster was with you before, and now you could go just about anywhere! You thanked him and he left shortly after. The next day, you chose to exercise your new privilege. Hesitantly, you put your hand on the doorknob and opened it. Terrified that someone was going to yell at you for leaving, you stood in the doorway for a few minutes until, after tons of scientists had walked by and said nothing, you decided it was safe and went out into the hallway. The door shut behind you with a loud slam, making you just about jump out of your skin.

 _Okay so the door’s loud… good to know._ You already mostly knew your way around the lab, so it wasn’t hard to find the library, where you decided to pick up a few more books. On the way to the cafeteria to get something to drink, you passed by Gaster and Alphys. They were walking pretty fast, and talking quietly; probably about something private and important. Your curiosity was piqued, but you didn’t want to follow them or eavesdrop.

The rest of the day passed by uneventfully, along with the next 3 weeks. You felt a lot better around Gaster now, the embarrassment had passed and you felt silly for ever being that bothered by nothing more than an experiment. In fact, you found yourself looking forward to more. So when he came into your room and asked if you’d be willing to let him run a few more tests, you grew excited. In more than one way.

This time, however, was far less fun than before. All he wanted was to learn more about your bone structure. He was a skeleton himself, but he found than your bones were different from his in many ways. For one, they were much harder. They also had to support a lot more weight, which intrigued him. Ghostly hands ran over your body, pressing against your bones and tracing them. In all honesty, it did hurt a bit, but you knew it would be over soon.

When he finished, you let out a sigh of relief and sat up. “Well that wasn’t as fun as the last one, in fact I’m kinda sore now.” You chuckled quietly.

“I didn’t mean to hurt you.” He continued, with a worried expression. “Why didn’t you say anything?”

“Meh. I figured it’d be over quickly and I want to be helpful.” With a shrug, you stand. “Is that all or was there more you wanted to test?”

“No, nothing more today. I learned quite a bit, thank you.”

You put your clothes back on and let him guide you back to your room. Once there, before leaving he asked you if you’d have dinner with him later and you happily agreed.

Even though you hadn’t been around him much the past few weeks, you have gotten to know him a bit and he’s been surprisingly kind and respectful. You wanted to learn more about him and spend more time with him. Silently, you vowed to do just that; to join him for meals when possible, and see about chatting with him when he was free.

The fear you’d felt when first falling down here had slowly been replaced by curiosity and interest, and you actually were treated better here than you were ever treated on the surface.

For now, at least, you were somewhat content.

**Notes for the Chapter:**

> Dunno if I'm very happy with this chapter, but like I said, the plot needs to move forward and all. There'll be smut in five or six, maybe both. :p


	4. Chapter 4

It was late at night, and you were tossing and turning in your bed. All the lights in the lab were shut off so it was pretty much black, though your eyes had adjusted and you could make out the shapes of everything in the room.

For a moment, you pondered if it would be alright to get out of bed and wander. _Gaster did tell me I could explore the lab on my own, now… but I dunno. It’s nighttime, so that might be bad…_

Closing your eyes, you tried stilling your thoughts, but just couldn’t do it. You laid like that for about another thirty minutes before sighing and standing up. _Whatever. If I get in trouble, I get in trouble. Just wanna go out and get some water or something._

As quietly as possible, you pressed the door open and stepped out, guiding the door shut quietly behind you. The two guards at your door said nothing, so you assumed all was fine and started making your way down the hall to the cafeteria. Your soft footsteps were the only noise echoing through the halls.

However, thanks to your horrible sense of direction combined with the darkness you found yourself lost. As you wandered the halls, you had a hard time not panicking. Darkness wasn’t something you particularly liked, but you could normally handle it. With a few deep breaths, you told yourself that everything was okay and that you’re safe.

A dim light began coming into view through the darkness and you continued towards it, filled with caution and hope. As far as you knew, everyone was sleeping either at home or here. Gaster provides all his staff with rooms if they need it, which you thought was pretty nice of him.

You were nearly at the door when something happened that surprised you.

“Shit!” A loud crash from the room along with a familiar voice made you stop in your tracks; your heart was practically beating out of your chest. If you weren’t mistaken, that was… Gaster’s voice. You supposed everyone got frustrated, but of all the things to hear from him you didn’t ever expect something like that. The sounds of him sweeping up glass and muttering angrily to himself reached your ears.

Hesitantly, you took a few steps forward and when you reached the room, knocked on the slightly ajar door. “I-is everything okay…?” Your voice was soft, worried that you’d get in trouble.

Quick footsteps approached the door and, sure enough, when it opened Gaster was standing there. It was obvious he was irritated. “What is it? I’m busy.” There was an edge to his voice you hadn’t heard before, which made you shrink back. His eyes were purple flames, meaning he was using his magic or was incredibly agitated. You were willing to bet it was the latter.

“I couldn’t sleep… was going to get water but I got lost and saw the light. But it didn’t sound like things were going so well, and I was worried…”

His face looked… tired. He was probably overworking himself. Every time he talked to you before, he was always well put together… how often did he stay up late like this? His eyes flickered and lost a bit of their intensity. “I… apologize, human. I didn’t realize it was you. I’ll go with you to get water, then we’ll get you back to bed.”

You shook your head, wanting to do something for him if possible. “C-can I help with anything? I heard glass breaking and… well if you need a temporary assistant I can try.”

The irritated look on his face faded, and was replaced with one of surprise, and slight annoyance. “There’s nothing to help with, really. Besides, I doubt you’d be able to help with anything even if I did have more to do.”

You two stood there in the doorway, looking at each other for a few minutes; you wanted to help him, to learn more about him and see what he was like when he wasn’t fully composed. With a loud sigh, he opened the door fully for you. “You’re not going to go back to bed, are you? Well that’s fine. Come on in, but watch your step. Don’t want my goddamn mistake to fuc-” He stopped and cleared his throat. “Anyways. Be careful.”

It was almost cute, you thought. “Hey, it’s… okay. I was just startled. Everyone gets angry and nearly everyone swears. You aren’t above emotions.”

The flames in his eyes flickered, as if he had blinked. “Well yes, you’re right. I made a stupid mistake while moving the mixture. After it’s cleaned up, I do have to replace what I ruined, so I suppose company would be nice.” The harshness had left his voice, but you could still tell he was frustrated. “That experiment had been coming along nicely, but it’ll take a whole month to get it back to this point. I still had observations to make. I can’t believe I was so careless.”

“Nobody’s perfect, it may have set you back but if you think one month is bad, I have a real lab horror story for you about something similar. My psych professor on the surface told me that once she was working in a lab studying the hormones of a type of rodent, and had been working on it for 5 years. One day someone was looking over her work and apparently, she’d been using a material for the cages that could affect the hormone levels and, therefore, the outcome. She hadn’t accounted for it because she forgot or didn’t realize or something like that. 5 years of research, down the drain in an instant.”

An incredulous expression painted his face. “You have to be kidding, that sounds awful…”

“Nope! Not at all. True story. One month is nothing compared to 5 years, you’ll catch back up sooner than you think.”

With a sigh, he nodded. “Yes, you’re right. I just wish I had been more careful. My supply of ingredients isn’t unlimited.” He continued cleaning up, sure enough there wasn’t much for you to do at this point so you leaned against a wall and looked around the room. It was fairly large, though the clutter made it seem much smaller than it actually was. This seemed to be Gaster’s office, there was a large desk in the center with papers strewn about it. A set of blueprints rested on a shelf against the wall, along with materials for… something. You couldn’t tell what. There was also one entire wall with shelves nearly up to the ceiling filled with various samples. There were stacks of books on the floor, and a table with various equipment rested next to you.

“Is this your office…?” Gaster nodded. “Huh. It’s messier than I would’ve thought.” He froze and it seemed like he was about to say something, but stopped and went back to cleaning. “No offense, clutter isn’t bad. Sorry if I upset you…” You grinned sheepishly at him. “Um… so what can I do to help?” You glanced at him quizzically.

“As I said earlier, all I have to do is replace that mixture.” He dumped the broken glass in the trash can, then went to his shelves and grabbed the materials he needed.

Unsure of what to say, you fell silent as you watched him work. After a few minutes, he spoke up again without taking his eyes off of his work. “I’ve been planning a new experiment. It isn’t quite ready yet, however it should provide a lot of information for me.”

“What are you hoping to test?”

“You’ll find out soon enough, have patience.”

You laugh. “Yeah, says the man who flipped out over having to wait another month.”

He frowned, “well of course it frustrates me, however I’m still redoing it, aren’t I? If I didn’t have the patience, I wouldn’t start over.”

A few more minutes of silence washed over the room. You couldn’t help but think about your concern for him, even if it was late and he was tired he didn’t seem like the type to make careless mistakes. He never had before.

“H-hey, Dr. Gaster, I know I’m just your test subject and all but… if something’s, uh, bothering you I’m happy to listen. You don’t seem to make mistakes often, so if you’ve been having a bad time with something then… I dunno. I just want to help. If not me, talk to someone you trust or… y’know, whatever. Take care of yourself is what I mean.” You shrug, trying to sound nonchalant despite being incredibly worried about him.

“I appreciate the concern human, but I’m not overworking myself if that’s what you’re thinking. Some monsters like myself need far less sleep than humans, and it’s relatively common for me to stay up late working on projects. The quicker things get done, the faster we can learn.” He paused for a moment, thinking about how to phrase what he wanted to say. “I messed up because I was distracted, my mind was elsewhere.” If you didn’t know any better, you’d think he was… blushing. The light purple on his cheekbones was faint, and faded away so quickly that it could’ve easily been your imagination.

Deciding to drop the subject, as it seemed to make him uncomfortable, you fell silent and thought about another conversation topic. “So what’re you making, anyways?” You took a few steps towards his desk and looked at what he was working on. The beaker was about a quarter full of some clear liquid; he put in a drop of something else clear, but when it hit the surface thin lines of blue and white spread out from the center where it had hit. The liquid now looked almost like it had veins in it.

“This is a personal project, however it’s incredibly important. I’m afraid it’s also not something I can give out any information about as of right now.”

“Ah… all right. It looks cool though, that’s for sure.”

Gaster laughed softly, “thank you, however whether or not it looks cool has little to do with the experiment. And despite being blue, I assure you that temperature-wise it’s actually fairly warm.”

You snickered. “That was kinda bad, with a brother like Sans I’d think you could do better. His jokes are sans-ational.”

The two of you threw a few jokes back and forth until he finished and moved the beaker to the shelf, this time far more carefully. It didn’t break this time, thank god.

You both left his office shortly after, shutting the lights off in his office and locking the door.

The walk back was fairly quiet, despite being with Gaster the darkness was still making you kinda anxious and upon realizing this, he held his hand up and a purple flame materialized above it, lighting the way. He took you to the cafeteria to get you water, then led you back to your room.

“Good night, and thank you for the company. It was quite nice talking with you.”

Thanks to the dark, he couldn’t see your face heat up. “No problem. I… I enjoyed myself too. Thanks for letting me stay with you.”

You laid down in bed and passed out almost immediately. Gaster watched for a while to make sure you were completely asleep, and when he was sure you were he left to get some sleep himself.

As he fell asleep, you were on his mind.

**Notes for the Chapter:**

> I really wanted to explore more sides of Gaster, such as what he's like when frustrated. I've had this idea floating around in my mind for a while now, honestly. I actually like this chapter quite a bit, though I know it can be improved. 
> 
> (And if you're wondering, I am going to include Alphys and Sans more in future chapters, and there will be other characters joining in too).
> 
> Also... That story about losing 5 years of research? Yeah, true story that actually happened to my psych professor IRL, and she told the class. I felt so bad for her, that would suck! I can't imagine how much of a pain in the ass that would be.


	5. Chapter 5

**Summary for the Chapter:**

> Gaster's curiosity gets the better of him, but he's not even close to used to this kind of vulnerability and is ridiculously nervous. Reader offers to sate his curiosity, though.

**Notes for the Chapter:**

> So initially chapter 5 and 6 were going to both be in one chapter, but I'd written over 3000 words and wasn't even halfway done so I thought I'd split it up. Plus I'm still working on chapter 6 and I don't want to make you guys wait forever for this. Hope you enjoy! ^^

Gaster sat in a chair in front of the computer, replaying the video of his second examination of the human over again. He didn’t know how many times he’d watched it at this point. Many, many times. That’s certain. Without a doubt, the effects of his examination had quite the impact… he wanted nothing more than to figure out what exactly happened, and how to possibly replicate it in other circumstances and through other methods.

Despite that, you had made it clear that you were uncomfortable with further experiments that went in that direction. At least for the moment. His cheek rested in his hand, elbow on the desk, as he kept his eyes glued to the screen. There was no need for notes this time. He’d written everything down the first few times then decided that, seeing as he had the whole video basically memorized by that point, he didn’t need to take any more notes.

It was certainly… interesting.

Regardless of what he tried, there didn’t seem to be a way to elicit those feelings in himself at least. He wondered if it was because he didn’t have nerves? But that didn’t make sense, as he could experience other physical sensations similar to yours, such as pain, just not this one.

At least, he couldn’t cause the feelings in himself… perhaps someone else could? He wanted a better understanding of why exactly it had bothered you after all was said and done. You had been right; in his mind it was nothing more than research. He wondered if he could ever understand why it had affected you so greatly.

Sure, monsters /could/ reproduce. Obviously. And it did feel good, from what he had learned; that being said, he’d always been too busy with his research and hadn’t met someone he wanted to experience it with. It never really crossed his mind until recently. And it wasn’t usually a physical thing, it could be but more often than not monsters only used their souls for this sort of thing. In fact, physical reproduction was impossible between monsters; not that some monsters didn’t try, it was pleasurable for most at the very least.

When the video was over, Gaster unplugged the USB, shut the computer down, and stood to leave the room.

Even though he went around nearly the entire lab, he wasn’t able to find Sans anywhere. It was frustrating to say the least; ultimately, he went into his brother’s room and put the flash drive down atop a quickly scribbled note.

‘I need you to watch the video on this flash drive and let me know what you think. I’m curious to find out more, however the subject is unwilling to participate in more tests like this for the moment. It’s vital that I glean all the information I can out of this, and a second observer may help. Look for anything that seems significant. My notes are saved in a file on there as well, so you’re free to read through those and add to them so long as you make it clear where my observations end and yours begin. Feel free to watch and discuss it with Alphys if you feel a third opinion will help, however I’d like to keep this video between just the three of us. It’s something that embarrasses the subject greatly, and I’d rather not have it spread around. I also ask that you remain professional about this. Thank you in advance.’

It was absolutely against Gaster’s better judgment to trust Sans with this; he was an excellent assistant, but he was also mischievous and had caused problems before. Usually minor, nothing that caused setbacks, but incredibly exasperating to deal with. Hopefully he’d behave himself. Gaster honestly did need another opinion, and couldn’t think of anyone to show the footage to otherwise.

With quick steps, he made his way to your room. Before approaching the door, he calmed his nerves. He tried to convince himself this was out of a desire for nothing more than knowledge and understanding, perhaps a way to gain your trust more as well; he told himself this was just to find answers.

Gaster always knocked before entering your room, which you thought was nice. It gave you some warning and a moment to let him know if you needed privacy right then. Hell, he gave you more respect than your parents had in that regard!

After a few seconds, he stepped in. “Good evening. I understand that it’s later than usual, but I would like to try something. It will be slightly different from the typical tests, however it will give me a better understanding of you in general. I’m uncertain about whether you’ll be fully comfortable or not, but everything about you interests me and I would like to learn all I can if you’ll allow me to. Some of your emotional responses have intrigued me and I'd like to study something specific.”

“Uh…” There was an awkwardness in his voice that you hadn’t heard before, and he was talking faster than usual. His normal speech was soft, and well-thought out; this sounded more like rambling almost. You didn’t know why, it could have easily been your imagination, but it still intrigued you. “What did you have in mind?”

His eyes darted around the room, and he looked like he was trying hard to come up with a good answer. That definitely worried you. A moment later, he looked back at you with a seemingly forced smile. “Never mind. I’m… sorry to have bothered you. Have a good night human, I’ll see you in the morning.”

Before you had even processed what he’d said, the door was already shutting behind him, leaving you in the room alone to wonder about what had just happened. _That was weird…_ With a shrug, you went back to drawing. Whatever that was about, it probably wasn’t a huge deal. If it was, he’d come back and talk to you about it eventually.

Meanwhile, Gaster left to go work on his secret side project.

He had to get his mind on something, anything else; and at least working on _that_ would be beneficial, rather than sitting around getting all worked up over something that should be minor to him.

Hours later, after the lab had gone dark, you couldn’t stop yourself from remembering what happened earlier. _What the hell did he want to try? Maybe he’s still here. I kinda want to check… hopefully it goes at least partly as well as last time._

With that thought in your mind, you left to try and hunt down Gaster’s office once more. When you got to it, the lights were off and the door was locked. _Damn… Since I’m already out here though, it wouldn’t hurt to have a look around, right?_

Eventually you stumbled upon a room that had an incredibly dull light coming out of the window in the upper part of the door. A sign above the door simply read ‘COMPUTERS’. Someone was in there… maybe Gaster? Your hand rested on the doorknob, but you hesitated. _And what if it isn’t? What if someone else is here?_ There wasn’t any noise coming from the room, but the light never faded.

Preparing yourself for whoever – or whatever – you might find, you pushed the door open as quietly as you could. To your surprise, the door was perfectly silent as it opened and shut.

After stepping into the room, following the light wasn’t too hard. It was coming from the far right corner. As you got closer, you could make out the shape of someone shifting in the chair, and the video made itself clearer and clearer.

Your eyes widened and blood rushed to your face when you instantly recognized both the room and the scene that was taking place on screen.

Whoever was watching it hadn’t noticed you yet, and you could’ve easily slipped out; however despite being horrified that that had been recorded, you couldn’t help but wonder what was even happening.

One of your shaky hands rested itself on the back of the chair and you quickly spun it around. Staring back at you in a mix of fear and surprise was Gaster. He had to bite back a scream, you didn’t notice it but you’d scared him pretty badly.

“W-w-w-what the hell, Dr. Gaster? What is this? What are you doing? Why?” You couldn’t tell if you were more furious or embarrassed.

“All experiments are recorded for future notes. What are you doing out of bed, _again?_ That's the second time this week! I thought I was the only one awake in the lab. I’ll make sure the guards know to keep you in your room at night from now on.” One of his hands quickly pulled away from where you guessed his sternum was and his face was flushed purple; he looked like a kid who’d been caught taking cookies from the cookie jar.

“…Do you realize what this seems like? I thought you wanted to learn, not be a creep!”

“No! No, no, I swear that’s not at all what’s happening. Can I explain?” You crossed your hands over your chest and glared at him, silently, waiting for his explanation. “I was… curious. Monsters are able to enjoy things like that supposedly. But… only some. And I’m either not one of them or I’ve been doing something wrong. I was watching this again to see if there was anything I was missing. I want to understand why you reacted the way you did, both physically and emotionally.” His eyes were turned to the floor, hands wringing together in his lap.

“So… Wait, wait, wait. You don’t know if you can even get physical pleasure? You've never even really tried before? Is that why it’s something you seem so interested in?”

He didn’t answer, nor did he look up. You hadn’t seen him this upset in… well, you’d never seen him like this. It was tough to stay mad at him. Despite the fact that he towers over you most of the time, can use magic, and has a large amount of power along with nearly unrivaled intelligence – everything you’d seen so far clearly didn’t even scratch the surface on either count – he looked absolutely ashamed.

A sigh escaped your lips. At least he had the decency to feel bad about getting caught if nothing else. “Goddammit. I really want to be mad, but now I just feel like I’m kind of a bully.” Raising an eyebrow at him, you held out your hand. “C’mon. I’ll see what I can do about helping you with this if you want. Like an experiment, right? But only because I feel bad for you and I’m pretty pissed. I want you to be as embarrassed as I was.”

His expression became confused as he nervously glanced back up at you, “you’d be okay with that?”

“Well, uh…” You suddenly realized exactly what you’d just offered him, and your face instantly went beet red. “I… I guess? If you guide me. Or… whatever.”

After a few moments of silence, he stood up. “W-well, then. We should probably go to the other room for this. If you still want to, that is.”

When Gaster noticed your nod, he shut the computer off and took the backup flash drive out, slipping it into his lab coat pocket. The awkward silence between you two was filled with the sound of footsteps; neither of you could look at the other. He had created another magical flame light to guide the way again, but it was between the two of you this time instead of on the other side of him.

Upon arriving in the examination room and shutting the door, you and Gaster both just kinda… stood there. Neither of you really knew what to do.

You couldn't help but worry about what you'd gotten yourself into this time. 

_Oh boy... this is gonna be... different._

**Notes for the Chapter:**

> I had a lot of fun with this. I really like flustered Gaster. But I'm trying to write Gaster in this story different from the version of him I've been writing in my other stories so I tried to make him much more composed. I'm really attempting to write a more dominant Gaster than I'm used to, so it's a bit hard to figure out how to get that dynamic working at the moment.
> 
> I think this is my favorite chapter so far just because I love the computer room interaction. I thought of it while writing and just couldn't say no. And I like tsundere reader to be honest, so definitely expect more of that. And expect Sans being a tease soon, he's got some great material now after all! Especially with the recording of what's gonna happen next chapter ;)
> 
> Get curious about Gaster's side project too, things are gonna be fun from here on out~


	6. Chapter 6

**Summary for the Chapter:**

> Reader learns more about Gaster.

Gaster's voice was fairly quiet, almost a mumble in fact. “If you don’t want to do this, I won’t force you to.”

“It’s… f-f-for, for the sake of research. And stuff. Anyways I’m curious. So. Are you going to, um, tell me what I’m supposed to do…?”

“You’re curious about this? This kind of… situation… has been on your mind?” He tilted his head slightly to the side, puzzled.

Sputtering, you shook your head. “NOT what I meant! I just… I’m curious about you in general. Like… how you work. How you move. Other things like that. T-the same kind of curiosity you have about humans…”

“O-oh. I’m sorry, I assumed.”

“Don’t worry… I just… I should’ve been clearer I guess? Can I… Can I try and figure you out before jumping right into things…? There’s a lot I want to know, and explore… Not in a weird way! Not weird at all. Uh… yeah.” You swallowed hard, hands behind your back and eyes on the floor.

“Yes, of course. If you’d told me that you were curious earlier, I would have been fine letting you ‘explore’, to use your word for it.”

The both of you still just stood there. Silence filled the room.

Gaster was the first to move. “Well, I suppose that we should just. Start.” He slowly sat down on the table where you’d sat many times by this point.

You shook your head, “wait, wait. You always made me take my clothes off first. So go on.” Despite your unease, you wanted this to be just as uncomfortable for him as it had been for you. It’s true that you were curious about his body, but that didn’t mean you couldn’t at least enjoy this power while you had it.

Standing back up, he hesitantly removed his lab coat and folded it up neatly, setting it next to the sink. It seemed like he was stalling, but you would put up with it for now. Next, he pulled off his turtleneck, revealing his ribs and part of his spine. That was folded as well, and set gently on top of the coat. He bent down to take off his shoes and socks, putting them beneath the table. You could see the curve of his hip bones poking out of the top of his pants, which took him longer to remove due to his slightly shaking hands.

It wasn’t like you expected anything different. In front of you stood what basically looked like a relatively normal, human skeleton; albeit a tall one. His rib cage was filled with some kind of misty, dark purple substance. _Magic, probably._ If it weren’t for the mist, you could’ve mistaken him for a prop in a science classroom. Seeing him like this was… strange. You motioned for him to sit down, which he promptly did.

Gaster seemed far more comfortable than you, even though in reality you both were insanely anxious. He was just better at disguising it.

“If I… uh… If anything hurts, just… just tell me. I don’t wanna hurt you, but I’m not gonna hold back unless you let me know I’m going too far. Okay?” You wanted to make that very clear to him.

“Of course, I understand.”

It took you a few minutes to decide where to start. Ultimately, you decided to start with his face and work your way down. One of your hands ran slowly along the side of his face, thumb tracing the outline of his eyesocket and then down the scar to his mouth. “How did you get these marks…? Are they scars?”

You noticed a pained expression on his face as you asked, and almost immediately regretted it. It took a few minutes for him to gather his thoughts and collect himself before he could answer. You were about to apologize for asking, but he beat you to it, responding right before you were about to open your mouth. “Well, I got the scars in… an accident. There was a prototype of the core in development at the time, but we all had some problems getting everything working. As a result, there was a meltdown and the core exploded. Sans was there and I protected him, though in doing so I was hit with some pieces of the machine. I don’t regret saving him, he was only a child then, however it all would’ve been preventable had I only been paying more attention. I wish I had been more thorough to begin with.”

Silently, you watched his expression. It was a mix of regret, irritation, and guilt. “It’s okay. It wasn’t your fault, Dr. Gaster. Shit happens, and what you did was incredibly brave. My older brother wouldn’t do that for me, Sans is lucky to have you. And you’re smart, I’m sure you put in failsafes on the final version or something. So don’t beat yourself up over it, okay?” You weren’t really sure what to say, but you didn’t want to bring up such bad memories without at least trying to help him feel better.

He didn’t answer, and you didn’t add anything either. There was nothing to say, no way you could keep him from blaming himself. At least in this moment. So instead, you slowly continued. Your thumb pressed lightly against the corner of his mouth, which he opened for you. Inside was pitch black. You never really noticed before, but he had sharp fangs on his top row of teeth; the rest of his teeth looked oddly normal. Cautiously, one of your fingers ran along the edge of one of his fangs. Not hard enough to hurt, but hard enough to get an idea of how sharp they were. It seemed strange, they were much duller than they looked. Their appearance was pretty impressive, intimidating even. But upon feeling them, it was clear that you weren’t in much danger even if he were to bite down.

Eyeing the blackness inside his mouth, you pressed a finger against what looked like a semi-solid surface; your finger sunk in slowly, much to your surprise, and was surrounded by something… warm, something thick. It made the tip of your finger go slightly numb, which concerned you enough to make you pull your finger out of his mouth. You felt a tingling sensation left over on the tip of your finger, and saw that a bit of whatever was in his mouth had stuck to your finger; though it dissipated almost too quickly for you to even see it. Gaster answered your unspoken question with a simple explanation.

“Magic. That’s part of the magic that makes up my body. It’s how I absorb nutrition, how I eat. You weren’t in any danger though, I have full control over it. In case you were worried.” You nodded and thanked him for telling you, since what he told you actually answered quite a few questions that you had.

Next, you brushed your hand against his clavicle lightly and saw him twitch. Apparently he felt something. Wrapping your hand around it, you allowed your fingers to press into the bone slightly; this made Gaster gasp quietly. His bones were incredibly soft, smooth, but otherwise didn’t seem too different from your own. “How does that feel…?”

He was silent for a moment, lost in thought, but he did answer you eventually. “It feels… quite nice, actually. I don’t understand. When I tried that, I felt nothing.”

You pondered this for a moment. “Well… uh… I may be assuming a lot here. But… you said I’m the strongest here, right? A strong, human soul, combined with the intent to harm can kill nearly any monster in one strike is what you’ve told me… but what if a human has a different intent? I don’t want to hurt you, or anyone, nor have I ever wanted that. Maybe because my intent is to learn, and to see if you can enjoy this, it actually feels good. Whereas when you tried alone, you couldn’t get that same effect or something…? Because it was from you and not someone else? I dunno, just… just a thought.” The hypothesis sounded better in your head, but Gaster thought it over and agreed that it was a possibility. He wasn’t entirely sure though, as there wasn’t enough evidence one way or another… yet.

As your hands lightly ran over the outside of his ribs, you could feel him shudder occasionally and soft gasps escaped his throat. He never told you it hurt, though, so you didn’t stop. One of your hands moved to run along his arm, and down to his hand. Once at his hand, you held it up closer to you and noticed there was a gaping hole in the palm. You wanted to ask, but since you already brought up some bad memories you didn’t want to risk asking.

Still, you were curious. You ran a finger along the inside of the hole, which caused Gaster to tense up and you immediately stopped. “S-s-sorry, I, uh, are you okay?”

He nodded, “yes, I’m… perfectly fine. I apologize. That’s apparently fairly sensitive. I had no idea, to be honest.” A soft grin rested on your face, relieved that you hadn’t hurt him and excited that you found something like this. You told him you were going to find out exactly /how/ sensitive, and he just looked away with a purple-tinted face in response.

With only a small amount of hesitation, you drew his hand up to your mouth and used your tongue to trace the hole. He inhaled sharply (you had yet to figure out how he could breathe considering it didn't seem necessary for him) and shifted on the table. You pulled your mouth away slightly. “What was that like? Good?” He didn’t answer verbally, but the darkening purple on his face made it pretty clear. You continued to run your tongue slowly along the edge, drawing a shaky, content sigh out of him. “I’ll take that as a yes, then.” It seemed strange to you, that something like that would be sensitive.

It gave you an idea, though. Reluctantly, you put his hand back down and let it rest at his side. Pulling his face close to yours, you planted a kiss on the side of his mouth and drew your tongue upwards along the scar connecting to it. That made him gasp in surprise, but a hint of pleasure laced his voice. You were really glad this was working. Considering he’s made out of bones you weren’t entirely sure what to do.

“I still have a lot of questions about your body, but I’m more intrigued by your reactions now.” You whispered next to where his ear would be before putting a hand on his sternum and rubbing small circles into the middle of it lightly with your thumb. “Assuming you still… are okay with… y’know. This.” Despite the fact that you were starting to enjoy yourself and were excited to learn something new, you were still worried.

“Don’t worry so much, I promise I’ll let you know if I change my mind or if something bothers me.” Though he seemed composed, his voice was shaking slightly. The uncertainty in his voice caught you off guard, but you decided that it was probably just nerves; he did say it was still okay, after all.

Your fingers tentatively brushed against his top rib as you ran your hand from the center to the outside slowly, making sure to feel all the small dips in the bone. The texture was strange, you hadn’t felt anything like it until now. It was rough, and there were what felt like shallow cuts covering the surface of his bones, yet there weren’t any sharp edges nor was the feeling against your fingers painful.

Gaster was trying to stay quiet and let you work your way over his body in peace, that and he was finally starting to understand your embarrassment, however keeping himself silent was getting harder with every time your hand brushed across a particularly sensitive spot. When your hand stopped moving he took a deep breath, relieved that you were giving him a second to relax.

It wasn’t long, though. You had moved your hand and wrapped it around his spine, allowing your fingers to push lightly into the bone and causing Gaster to desperately do his best to hold back a moan. You clicked your tongue in disapproval. “Hey, don’t get all shy on me now. If you… If you’re enjoying this, uh… Well that’s the point. So. Just calm down and let it happen.” Your other hand reached around to his back and traced the edges of his shoulder blade, which you then brushed down the back of his spine delicately.

For a second, he looked embarrassed, but the quiet sigh that came out of his mouth silenced any protest he would have made. He relaxed into your touch as well, which made you blush. Seeing him like this brought a gentle smile to your face. It wasn’t often that he seemed so at ease, he was always rushing about and had something to work on. Your lips pressed against his cheek as you used one hand to massage his spin as best as you could. It felt a bit awkward initially, but you were able to get a good rhythm going and you figured you were doing a good enough job; Gaster’s eyes had shut and his body had further softened, one of his hands was even resting in your hair. You would’ve thought something like that would hurt, but he was incredibly careful not to scratch you or be too rough and it actually felt rather pleasant.

“You’re… made out of magic, right? How does that work, anyways? Is that the misty stuff in your chest? Why is it visible there, but not anywhere else?” Your curiosity was starting to get the better of you.

He nodded without opening his eyes, and in a soft, soothing voice responded. “Yes, that is the magic that holds me together. Monsters aren’t physical in the same way that humans are, despite the fact that it appears that way. This body isn’t nearly as set in stone as a human body would be, it’s a manifestation of my soul, or more accurately, an extension of my soul. The mist, as you called it, is where the main source of my magic is; it looks like that in parts of me that have the highest concentration of magic, which can change depending on various factors. Typically whether or not I am using the magic, and what I’m using it for. The location, appearance, and intensity can also be influenced by mood, however. Do you understand?”

“Y-yeah… I think? That actually kinda makes some sense, though I don’t think I fully get it...” You were still confused, but he hadn’t done a bad job at explaining; it was just so surreal in a way, everything about this seemed so strange that it was hard to wrap your head around it all.

Deciding you’d asked enough questions for now, you placed your lips against his neck and bit the vertebrae there lightly, which coaxed another small, calm noise out of his mouth. His eyes opened and the pinpricks that were normally white had a small purple hue to them. “This on its own feels rather nice. I’m unsure if this is what you felt, in fact I highly doubt it, however I’m fairly certain now that your idea is correct. It must have to do mainly with intent and the strength of a soul.” He averted his eyes though, and the purple returned to his face. You noticed for the first time that when he blushed, the light shade of purple came up all the way from the magic inside his rib cage, lighting up his neck slightly; it caused his cheekbones to almost glow. _I didn’t have an explanation before… but that’s pretty cool. That must be what he was talking about with magic changing based on mood or whatever._

“I think that, as long as it isn’t too disappointing for you, I’ve gotten all the information I need.” You could hear a hint of uncertainty in his voice and you didn’t want to push him; after all, he hadn’t pushed you further than you were okay with.

Slightly saddened, you moved away from him. “Yeah no prob. I learned a lot too, so… thanks. But if… if you ever want me to do that again, maybe… m-maybe even going further, I’d… well I wouldn’t mind much.” Your face was bright red, but if Gaster noticed he didn’t mention it.

“Ah… Okay, I’ll be sure to let you know.” He coughed lightly in embarrassment and stood up, redressed, and thanked you for the help. After that he brought you back to your room again, which reminded you of what he’d said earlier about revoking your night-time exploration opportuities.

“Uh… Dr. Gaster? You… You didn’t mean that thing about locking me in at night, right? I kinda like exploring and… if I need water or whatever…” After having your freedom, you didn’t want any of it taken from you.

One of his brow bones raised and his expression almost looked playful. Teasingly, with his arms crossed over his chest, he answered you. “Hm… I’m not so sure. You don’t exactly behave yourself.” You were about to protest, but he continued before you could get a word in. “I suppose I won’t remove your privilege, but please, do try to keep out of trouble from now on.”

You couldn’t help but snort indignantly. “Hey, you were the one being a damn perv. Weirdo. I wouldn’t have caught you if you were doing normal stuff!”

He just chuckled. “Well I suppose you make a compelling argument, though I will rewatch my experiments as many times as necessary. There’s absolutely nothing strange about reviewing the data. On a more serious note, please, refrain from getting too curious. There are far too many things here that could get you very hurt if you stumbled across them accidentally. Okay?”

“Yeah, yeah, yeah.” You rolled your eyes, “you don’t want your test subject getting hurt. I gotcha. You should behave yourself too, next time I catch you like that I’ll be truly upset. And you don’t wanna face my wrath.”

“Oh yes, I’m so very terrified of your wrath.” You did your best to ignore the fact that his voice held a subtle hint of sarcasm.

“You should be.” You stuck your tongue out at him for emphasis. Childish? Perhaps. But it was late, you were tired, and you felt like it was a good idea.

His laugh was still gentle, but his smile was wider than before. “Alright, alright. It’s quite late, and we have a big day tomorrow. Please, make sure to get enough rest now. Good night, human.”

“G’night, sleep well doctor.” He shut the door quietly and you were left wondering what he meant. You almost wished you had asked, however you probably didn’t want to know just yet. With a big yawn you crawled into bed and slept better than you had in a long time.

**Notes for the Chapter:**

> Welp I promised you guys dominant Gaster, but... this chapter he’s not super dominant. That’ll change in future chapters though, don't worry~ I wasn’t sure how to incorporate that well in this specific case but dammit I tried and ultimately I’m okay with how this turned out. It took me way longer than it should’ve, though. Speaking of I’m sorry it took so long ;_; Wasn’t really writer’s block per se, more that I wasn’t quite sure how I wanted to portray this for sure so I spent a lot of time working out the kinks. (Pun intended of course.) Sorry if the chapter's a bit rushed, though... I had trouble with it, way more than I expected.
> 
> Um, so, this isn’t super smutty either. It was going to be but I wanted something cuter for now because it seemed to be a better direction to take this scene in. Sometimes while I’m writing I wind up going a different direction than I planned because it flows better and this is one of those cases. I know I promised smut this chapter, but I liked this a lot better so plz don't hate me there'll be much more smut soon!! D: And there will definitely be a part 2 of reader exploring Gaster in the future, for sure!
> 
> Hopefully it wasn’t too awful to read. Next fun scene will be in the shower but it’ll be another chapter or two of plot first :p Don’t worry; shower kink was already on my list and I will get to writing it soon, oh so soon ;)
> 
> Comment any other suggestions anytime, for smut or plot, I'm open to writing just about anything involving Gaster because I'm a dirty sinner and I love every minute of it <3


	7. Chapter 7

He’d warned you that today was a big day, a busy day. You knew he’d been planning a new experiment for a while, but you wished that you had known at the time what he had in mind; this was way more than you had expected. He asked you many, many times whether it was okay and explained that it would be painful, along with describing all the potential outcomes he could think of. He wanted to have your full cooperation and no ambiguity about your consent, considering this was a pretty monumental experiment.

Your emotions were a rollercoaster.

On the one hand, you trusted him and liked where this was going. On the other, you were terrified. Part of you was pissed and, for the umpteenth time since you’d fallen, you were wishing that things had gone according to plan when you jumped. The strongest emotion, however, was definitely the mixture of anxiety and excitement; the butterflies in your stomach, your heart beating faster, and the knowledge that something incredible, yet uncertain, was going to happen soon.

Still, what was happening here and now was happening and you’d agreed to it, anyways. Sure, it wasn’t like you or Dr. Gaster had any idea what the true results would be of this test, but you now wished that you had asked for him to try something else, anything but this, today. Hearing him talk about it didn’t come close to how it actually felt.

He had wanted to find out if it were possible to imbue a human soul with magic. He was aware that some humans could use magic and some could not, but he had no idea why and wanted to get to the bottom of it.

The experiment was simple; take a small amount of his own magic, mix it into some determination so that your soul would handle the foreign energy better, and inject the concoction into your soul directly. He warned you beforehand of the dangers, things that could happen if your soul rejected the magic and that it would probably be incredibly painful, but you were curious too. And if this worked out the way Gaster thought it might, you’d be a magician! You always wanted to be able to use magic and bend reality to your will; but you’d always thought it a silly fantasy.

A fairy tale.

But you were kind of in a fairy tale anyways, all things considered. You couldn’t be surprised by much else at this point.

Gaster knew that the king would never approve of this research, giving humans who already have an advantage even more power was too risky in his mind, but Gaster trusted you and, for better or worse, his curiosity got the better of him (as it so often did).

Besides, the amount of magic was so small that it’d be hard for you to hurt anyone; he’d also prepared a device to hold and restrain you in case anything went wrong. That was only in the worst case scenario, he hoped to not have any use for it.

Despite being intelligent, some things like the social and emotional implications of actions went right over his head. Something like sharing his magic with you, putting it directly into your soul and thus connecting the two of you in an incredibly intimate way, hadn’t occurred to him; nor did he realize that it could be creating a link that perhaps shouldn’t be made. To him, it was just another experiment to understand how certain humans can use magic and others can’t.

It was easy to overlook what he considered to be little things like that.

Gaster’s hypothesis was that by infusing your soul with magic, you would be able to actually use magic in the same way that monsters do; albeit much weaker, since you had no experience and it was borrowed magic. He thought that maybe, after a while, your soul might produce its own magic too after being introduced to it. But that was probably a long shot, so he didn’t put it down in his notes, nor did he mention it to you.

“I need you to stay relaxed and breathe deeply, okay? This will hurt, however I’m going to be as gentle as I can.”

“Yeah, okay. I trust you.”

You hadn’t seen your soul until now; it was stunning. You’d never expected souls to actually be a real, physical, legit thing! Even when Gaster mentioned souls, you always assumed he was being metaphorical. Humans talk about them in religious contexts and such, but this was… indescribable. Seeing it right in front of your eyes… There’s no way you could deny that souls exist at this point. It raised quite a few questions in your mind that you hadn’t thought to ask before.

The heart-shaped soul floating in one of Gaster’s hands was glowing with a mixture of cobalt blue and black dancing together; there was a thick, gold outline around your soul. It looked like something out of a painting. According to Gaster, that particular shade of blue tended to represent tranquility, willpower, and patience, while the black often had to do with defense, wisdom, and protection. Gold related to things like luck, abundance, and prosperity; though, he clarified that everyone’s soul manifested colors based on the person’s own perceptions of what those colors mean. Therefore, there’s no universally correct way to interpret what a person’s soul is actually like.

“Every soul is different, and every soul changes and grows as the person it belongs to experiences life. A soul can change drastically in the span of only a few moments, depending on the changing circumstances.”

He explained this all to you as he prepared, though watching him work wasn’t much fun. That needle looked far too big to be comfortable… You allowed his voice to distract you from what was actually going on, and you managed to learn quite a bit.

“You are going to be just fine, so please stay relaxed and don’t be afraid.” You just nodded, his voice calming you. As the needle approached your soul you cringed and shut your eyes tightly, waiting.

Him saying that it would hurt, well, that was quite an understatement. You could hardly breathe as pain coursed through you. The room suddenly felt very far away, you heard Gaster speaking to you but couldn’t understand what he was saying through the fog in your mind.

Someone was screaming. Was it you? It didn’t seem like you, but that was the most likely conclusion. The pain was a dull ache by now, you felt separate from what was actually happening. Somehow it made things easier, though. Even if you were feeling the pain, something in your mind or soul or whatever was protecting you from being aware and experiencing the worst of it.

Everything was so distant. The voice was getting louder, but still was hardly a muffled whisper in your ears. It held far more concern than you had first thought.

Your head was pounding and you felt suspended in empty blackness. Had it been years or only seconds? It was impossible to tell. Eventually, though, you felt yourself floating back to reality. You had no clue what had actually happened in that time, and were afraid of what you might see.

Luckily, as your eyes opened and you were able to focus on the room, it was clear that things had gone… at least somewhat according to plan? Nothing was ruined, anyways. Everything was in its proper place, and your soul was back where it belonged. You felt a bony hand resting on your cheek and saw that it wasn’t attached to anything. Probably his way of monitoring you without having to look or something, it felt nice compared to the nearly overwhelming heat radiating from your chest throughout the rest of your body. Gaster was rushing around the room grabbing various things from shelves, and it was clear he was at least partly panicking and looking for something specific.

He stopped dead in his tracks a few seconds after your eyes opened, and the flames in his sockets brightened as he almost immediately ran back over to you. “Are you okay now? I shouldn’t have been so reckless, this was obviously a bad idea. I’m so very sorry that I hurt you, are you still in pain anywhere?” He spoke quickly, words pouring out of his mouth one after another without much of a break in between. His voice still sounded muffled, quiet, you were barely able to understand his words.

As soon as you started talking, Gaster fell silent and watched you closely, eyes flickering rapidly.

“Uh… Well I’m probably fine now. I think I dissociated or something? Because after the needle went in I didn’t feel much at all… but I could hear what was happening. Was… was I screaming? Never mind I think I know the answer to that.” You grimaced, the pounding in your head had only gotten worse. “Welp, my head’s killing me and I feel pretty warm… like it’s really fucking hot in here or something. But it’s not from outside of me? I dunno how to explain it. But otherwise I think I’m fine…? What should I be feeling right now?”

Gaster sighed in relief, “I’m glad to hear that you’re alright. Still, I shouldn’t have tried this. All the same… what’s done is done, and hopefully there’s something to be learned from this.” He sounded like he was almost talking to himself as his voice trailed off. “Oh! Yes, here, I almost forgot.” A bottle of water was placed in your hand, “drink as much of this as you can. It’s just water, however it should help.” You did as he asked and, when the bottle separated from your mouth, you found that you must’ve been thirstier than you thought; half the water was now gone. “That warmth is likely your soul reacting. I’m unsure about how long it will be before we see any results, but your soul accepted the magic which is a fantastic sign.”

You didn’t bother trying to follow what he said after that; your head felt fuzzy and it was hard to focus on much of anything. Despite that, you did manage to catch something about how he’d want to observe you more closely over the next few weeks.

Normally, his voice calmed you, however now it just made you agitated. You cut him off, “hey, I’m curious about this too, but do you think you can hold off on all that talking for now? Write it all down or something… I don’t care. But I can’t stand hearing you talk right now. It hurts and it’s irritating.” You hadn’t meant to be that harsh, but it was hard to really be nice when all you wanted was silence.

Instead of saying anything in response, Gaster just nodded and looked at you apologetically. He held his hand out to help you up, but you batted it away and stood on your own. For a split second, he looked hurt, but you paid it no mind.

He guided you back to your room and, when you both got there, you found a second bed in there. Gaster opened his mouth to say something, but instead thought better of it and wrote something down on his notepad. He gave it to you to read after he finished. ‘I need to monitor you for the next few weeks. If something goes wrong, everyone here could be harmed, and I can’t allow that. I didn’t think to mention it before but I’ll be staying in here for a while.’

“Wow, really? Coulda told me that beforehand… thanks a lot. Whatever though. Do what you need to do.” Part of you felt bad for talking to him like that, but the other part of you was stronger; and growing increasingly irritable. You didn’t quite feel like yourself, but you figured it was just a side effect and hoped the feeling would wear off soon.

**Notes for the Chapter:**

> I had planned for this chapter to have the shower scene in it, but this idea came to me and I just... I love it. It's a much better direction than where I was going to take the story originally. So prepare for trouble! (And make it double!) Uh sorry, wrong game reference. Anyways. Hopefully others are as interested in this as I am. XD I've got one other chapter coming tonight for sure, and possibly a third if I can fix it up properly.


	8. Chapter 8

**Summary for the Chapter:**

> This chapter starts from Gaster's perspective, then swaps to reader's. It's pretty obvious where it changes, but I just wanted to make that clear right off the bat.

It had been two weeks, and I could tell that there was something distinctly different about the human. I couldn’t quite put my finger on what; the only obvious sign was their increasing agitation and frustration. I was beginning to wonder if I should restrain them, however I didn’t want to do that unless I had no other options.

I ate with them, slept with them, talked with them, walked with them. They were clearly tired of me shadowing them, and tired of having to come with me whenever I went to check on something, but there was no other option really. No other safe option, anyways.

A few days prior I had wanted to ask about their behavior, yet I couldn’t quite bring myself to do it. They didn’t seem to want me to know anything, and I was hoping they would calm down after a few days but no such luck. They also seemed to ignore me when I talked, or perhaps they were having trouble hearing me.

Night seemed to be a good idea for timing, as they were more apt to open up then. I was uncertain as to why, but it seemed most humans were this way from what I’d observed in the past. So, I mustered up my courage and waited for the day to end.

…

They finished changing and laid down on their bed, pulling the covers over themselves.

“How have you been feeling, human?”

“Fine.”

“Can you elaborate a bit? I only wish to help you and understand what’s going on in your mind.”

“Why?”

“Because I’m concerned about you, and I’m concerned about the safety of everyone here. I could try and help you if I knew what was wrong.”

They shrugged their shoulders in response and turned to face the wall. I sighed and stared at their back for a few moments. “I don’t know if you’re still awake or not, but I promise I’m here to help you. I never meant for that last experiment to go the way it did, and I apologize for hurting you.” There were two reasons that came to mind about why they were behaving this way; either I had upset them, or there was a negative reaction between their soul and the magic. I was hoping it was the former. That would be so much easier to deal with.

When I didn’t get an answer, I just mumbled good night to them and tried to fall asleep myself. Nothing worked, I was allowing fear to get the better of me; I couldn’t shake this sense of dread. As I watched the human, they rolled over onto their back. I could see their chest rise and fall as they breathed. Even that was interesting to watch. They looked so calm, so at peace, and yet I could feel something darker radiating from them.

It would be my fault if something went wrong. I should have been more careful and listened to Asgore. Of course he didn’t know about this, I’d be lucky if he found out and all he did was fire me.

But if this went well…

If this went well, we could understand and learn about the way certain humans utilize magic, which could help us find a way to not only defend ourselves, but potentially help break the barrier! Sometimes, risks had to be taken for the greater good. And no matter the outcome, I won’t allow anyone to be harmed.

There are safeguards in place and, should the human get out of hand, I can lock them up for a few days until they calm down. There is no way this will go wrong as long as I stay observant.

Most nights I stayed awake long enough to ensure that they were asleep, and woke up hours before them. I had to make sure nothing happened, but I couldn’t abandon sleep altogether as much as I’d like to. I would get sloppy and perhaps miss some important details. Tonight, however, I couldn’t have slept if I wanted to.

I knew there was something wrong. And I knew that I wouldn’t let it get worse.

 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

You’d felt very little since Gaster had injected your soul with magic. The only emotion that you felt anymore was annoyance, and you snapped at anyone who tried to interact with you. A quiet part of yourself, deep down, was trying to get this to stop, but unfortunately it was too weak and small, and you were afraid.

It would be so, so very easy to destroy everyone here.

That thought crossed your mind more often than you’d admit to in the past two weeks.

Gaster could obviously tell something was up, but that was his problem and not yours. You had no intention of telling him. More than anything, you just didn’t want to have to explain. The less talking you could do, the better.

Sounds had been growing more and more muffled as time went on, but your own voice was so grating, so loud, that you wanted to rip out your own vocal chords. All you could bring yourself to do anymore was sleep, most days Gaster would have to coax you into eating and even then you didn’t eat much.

You had felt this way before.

The small part of you that still cared was ashamed and afraid, worried that you’d do something you couldn’t take back.

You had begun to think that maybe, maybe life was worth it and you had been looking forward to every day recently. You didn’t want to feel like this again, and knowing you did made you angry, so angry. Angry with yourself, angry with your family, angry with your friends, angry with Gaster. Mostly you regretted getting comfortable here, when you should’ve known better.

_Dammit…_

Your art was getting more and more morbid by the day, to match your thoughts. You hated being in this place again, but there was nothing to be done about it and you hated that too.

One night, you had the opportunity to tell Gaster what was bothering you. He asked, probably worried, about how you’ve been feeling.

The darker part of you was stronger, and you brushed off his questions before pretending to fall asleep so you wouldn’t have to listen to him talk anymore. Something inside of you regretted not saying anything, though. As you drifted off to sleep, you thought about coming clean and being honest with him. It was just a matter of being strong enough to say something.

When you woke up the next morning, Gaster was (as usual) already awake. You were still too groggy to feel much of anything, and figured if you were going to say anything it would have to be now…

**Notes for the Chapter:**

> Ooh a cliffhanger ;) Wonder what's gonna happen...~ Seriously though I'm really liking where the story is going. I do like the sexy stuff but I didn't realize I'd get so invested in the plot here honestly. I want to be really mean with the next few chapters, explore some darker ideas and themes... but I don't know for sure. I love the fluff and the smut so it all depends lol.


	9. Update!

Hey readers! :) sorry I haven't updated in a while. I left - sort of last minute - to a program called Job Corps. I didn't bring my laptop and this site's blocked on their WiFi, unfortunately. :/ it's because of the porn on here, so I'm stuck using my phone to type this while I'm in town and have normal service. I'm writing chapters by hand and will add a real chapter as soon as I've got my laptop/a computer of some kind with MS Word and WiFi. XD sorry I couldn't say anything sooner, the last few weeks have been super hectic.

Stay patient! I am still alive and writing and interested in finishing this story :p


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